Wavelength dependency of soft tissue coagulation with a tunable cw laser

A CW Tm:YAG laser with a tuning range from 1.86 to 2.08 micrometers was used to create thermal lesions on chicken breast, calf liver, and porcine cornea. All tissue types were exposed to a constant irradiance (450 mW, 0.92 mm spot diameter, 0.5 and 1.0 second exposures) at five different wavelengths about the 2 micrometers water absorption peak. We estimated tissue absorption coefficients from the thermal history recorded by a 8 - 12 micrometers thermal camera. Our data confirmed that the absorption of all tissue types tested followed the water absorption curve. The effect of these differences in absorption upon the coagulation lesion size was evaluated by histologic measurements.